Solid inhibitor for pickling baths



252. COMPOSITIONS,

Patented Jan. 24, 1939 UNITED STATES SOLID INHIBITOR FOR PICKLING BATES Percy J. Cole, Philadelphia, Pa., assignor to The Barrett Company, New York, N. Y., a corporation of New Jersey No Drawing. Application April 29, 1938, Serial No. 205,002

18 Claims.

This invention relates to the art of pickling metals for the removal of scale, and more particularly to corrosion inhibitors and pickling baths containing the same.

Pickling solutions for removing oxides or mill scale from the surface of metals ordinarily consist very largely of dilute solutions of a mineral acid, such as sulfuric or hydrochloric acid, which is capable of readily dissolving the scale. However, the acid also attacks the metal to some extent so that considerable acid is wasted and a corresponding amount of metal lost. It also appears the hydrogen liberated by the action of the acid on the metal frequently has a serious embrittling effect upon the metal being treated. For these reasons, inhibitors are commonly employed in such solutions to decrease the action of the acid on the metal without greatly affecting its solvent action on the scale.

Many materials have been employed as inhibitors in pickling operations. For instance, certain compounds of nitrogen, such as the heterocyclic nitrogen compounds, e. g., compounds contained in commercial pyridine and quinoline, are

known to be effective as inhibitors in acid pickling baths. However, compounds of this type are usually liquids and must be marketed in the form of dilute acid solutions which are somewhat corrosive and therefore difficult to ship and handle.

It is an object of this invention to provide a solid, non-corrosive inhibitor for use in pickling metals. It is also an object of this invention to provide a pickling bath containing a corrosion inhibitor which may be used at high temperatures without lossof corrosion-inhibiting properties, thus effecting economies in time and savings in materials.

The corrosion inhibitor of this invention comprises the product of the reaction between a pyridine compound and maleic anhydride. The term com und is intended to include pyridine and its homologues such as the picoli es and lutidines, quinoline, isoqmngl ine and their homoragug'Zmfi igfimf these compounds, such as are obtained rom coal tar distillates.

The reaction product is formed by mixing a pyridine compound and maleic anhydride, and permitting them to react, the reaction ordinarily taking place with the elimination of carbon dioxide and the formation of a solid-product. & gqrgingio the preferred embodiment of this invmionaallatrveirhignboiling pyridine compoundisnseisfidfi a'sone boiling from about 200 to about lifjglg, and especially one boiling from abotit2 50 to abofitf350 C as it has been found such pyridine compounds give more effective inhibitors than the lower boiling pyridine compounds. For instance, very effective inhibitors may be prepared by reacting maleic anhydride with coal tar bases having a specific gravity of lip Q from about 1.061 to about 1.135, the major portions of which distill within the range of from about 200 to about 350 C. Thus the following coal tar base fractions are suitable for use in the practice of this invention:

Specific gravity at 15.5 C 1.061 1.095 1.120 1.135

Bulb distillation (of 100 cc.

sample):

134 103 198 259 C. 165 178 220 262. 5 186 210 220 266 208 236 242 272. 5 228 249 254 281. 5 238 255 264 286 243 261 275 302 246. 5 273 293 320 250 289 319 335 254. 5 310 347 349. 5 90 268 327 358 355 95. 295 345 Dry 305 345 358 356 Distillate to dry point. 97 cc. 95 cc. 90 cc. 91 cc. Barometer, mm 764 764 767 764 Preferably, about one mol of the pyridine compound is reacted with from about one to about two mols of maleic anhydride. The pyridine compound and the maleic anhydride are preferably mixed gradually in the presence of a solvent, and mixture then heated with continuous agitation. At the completion of the reaction, the solid cake formed may be removed from the reaction vessel, washed, and dried. The mother liquor may contain unreacted pyridine compounds; it preferably is mixed with the wash liquor used to wash the solid product and reacted with additional maleic anhydride to recover the unreactcd pyridine compounds and any dissolved reaction product present in the wash liquor. The mother liquor is preferably reused only once, as otherwise impurities tend to unduly accumulate therein.

The process of making the inhibitor may be varied to some extent. In place of the pyridine compounds listed above, other high boiling fractions containing pyridine compounds may be used; or relatively low boiling fractions, such as denaturing pyridine (B. P. 115 C.), may be employed, although less elfective inhibitors are produced thereby. The ratio of the weight of pyridine compound to that of maleic anhydride may be varied considerably, depending on the pyridine compound used; but there should be preferably about one to about two mols of maleic anhydride per mol of pyridine compound. The maleic anhydride m xe irec with the pyridine compound; or, the maleic anhydride may be dissolved in a solvent, such as xylol, benzol, etc., and the pyridine compound gradually added to the solution. The amount of solvent may be between two and eight times the weight of the maleic anhydride, but it is to be understood any other suitable proportion of solvent may be used.

The reaction may be conducted at temperatures of from C. to as high as the refluxing temperature of the reaction mixture. The time of reaction is dependent to some extent upon the temperature at which the reaction is conducted and to some extent upon the pyridine compound used, and may vary between one and 24 hours.

The products obtained in the practice of this invention are solids which may be easily ground to powders. They are wholly or partially soluble in water, depending on the pyridine compound used. Low boiling pyridine compounds, such as denaturing pyridine, give inhibitors that are completely soluble in water, whereas the high boiling pyridine compounds, such as those listed above,

give more efiective inhibitors which, however, are only partially soluble in water.

The following examples illustrate the preparation of corrosion inhibitors according to this invention. Parts are by weight.

Example 1.98 parts of maleic anhydride were dissolved in 200 parts of xylol and the solution was warmed to about 80 C. 150 parts of a coal tar fraction containing pyridine compounds and boiling from 198 to 358 C. were then gradually added to the solution over a period of about one and one-half hours with continuous agitation. The reaction mixture was agitated for a further period of about 8 hours, the temperature being maintained at about 80 C., during which time asolid cake separated from the reaction mixture. Carbon dioxide was evolved during the first few hours of the reaction. The cake was removed from the vessel, broken up, filtered, ground, and washed with about 170 parts of xylol. The washed product was then dried at a temperature of 40 to 50 C. for several hours.

Example 2.The mother liquor and the wash xylol obtained in the filtration and washing steps of Example 1 were found to contain unreacted pyridine compounds and some xylol soluble reaction products. To recover these substances, the mother liquor and 22 parts of wash xylol were mixed and heated to 80 C. 98 parts of maleic anhydride were then added to the solution with continuous agitation. When the maleic anhydride was completely dissolved, '75 parts of a coal tar fraction containing pyridine compounds and boiling from 198 to 358 C. were added. Agitation was continued for a further period of about 6 hours, the temperature of the mixture being maintained at 80 C., during which time a solid cake separated from the reaction mixture. Carbon dioxide was evolved during the first few hours of the reaction. The cake was then washed and dried as described in Example 1.

The acid pickling baths with which the corrosion inhibitors of this invention are used may be aqueous sulfuric acid solutions containing to 15% H2SO4, such as are customarily used in the pickling of iron and steel. Instead of sulfuric acid, other mineral acids, such as hydrochloric acid, capable of readily dissolving iron oxides may be used. The amount of corrosion inhibitor added to the bath for carrying out the pickling operation may be varied, but it has been found that between .005% and .04% of the weight of the pickling bath is suitable. Common salt may be added to the pickling bath, if desired; or the salt may be mixed directly with the solid inhibitors and the mixture used in pickling baths. The amount of salt so admixed may, for example, be varied between 50% and 200% of the weight of the inhibitor.

The pickling or cleaning operation may be carried out as in usual practice. The metal may be completely immersed in the pickling bath and then washed to remove the acid; or a solution of the bath may be sprayed on the surface of the metal and the acid subsequently removed with a spray of water. By either of these treatments it will be found iron oxides, rust, etc., i. e., those compounds collectively known as scale, will be quickly and substantially completely removed from the surface of the metal, while only minute amounts of metal will be lost.

The following tests illustrate the inhibiting properties of the products of this invention. In these tests, strips of steel measuring y x x 3" were placed in test-tubes containing 50 cc. of a 5% sulfuric acid solution containing an inhibitor produced by reacting maleic anhydride with a pyridine compound boiling from 200 to 360 C. The strips were first immersed in this bath for one-half hour at a temperature of 93 C. to remove the scale, after which they were washed with water, rinsed in alcohol, and dried by dipping in ether. The treated strips were weighed and immersed in the same solution and at the same temperature as above for one and one-half hours. The strips were then washed, dried, and reweighed to determine the loss in weight of metal. The tests were also conducted using a pickling bath containing the above inhibitor and common salt; furthermore, tests were made using a pickling bath containing no inhibitor or salt. The results of these tests are shown in the following table:

The corrosion inhibitors of this invention may be used for purposes other than the pickling of metals. One phase of this invention involves the provision of mineral acid solutions which contain inhibitors in such an amount that corrosion of metal surfaces by the acid is prevented. Thus, in the transportation or storage of corrosive mineral acid solutions, a relatively small amount of one of the inhibitors may be added to the solution to prevent corrosion of the confining metal surfaces. The amount of inhibitor used will depend upon the nature and concentration of the acid.

The inhibitors of this invention may be mixed with foaming compounds such as saponin to produce preparations having combined foaming and corrosion-inhibiting properties. Upon the addition of such preparations to the pickling bath a layer of foam is produced on the bath which prevents, or minimizes to a great extent, the discharge of acid mist into the surrounding atmosphere and thereby materially improves the atmospheric conditions under which the pickling operations are carried out.

The inhibitors of this invention possess the desirable property of being non-corrosive solids so that they may be handled as a powder, and stored and shipped without any of the difliculties normally incidental to the use of inhibitors of a similar type, which are generally in the form of corrosive liquids and therefore dimcult to handle. In addition, these inhibitors may be used for pickling metals at temperatures as high as 252. COMPOSITIONS,

0. without aflecting the efl'lciency oi the inhibiting action, thus making it possible to conduct the pickling operations at such elevated temperatures with the consequent saving in time due to the increased rate of scale removal.

Since certain changes in carrying out the above process and certain modifications in the inhibitors which embody the invention may be made without departing from its scope, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A corrosion inhibitor comprising the product oi the reaction between a pyridine compound and maleic anhydride.

2. A corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a tar base, with evolution of carbon dioxide from the reaction mixture.

3. A corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a pyridine compound having a boiling range of from about 200 C. to about 360 C., with evolution of carbon dioxide from the reaction mixture.

4. A corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a tar base having a specific gravity of from about 1.061 to 1.135, the major portion of which distills within the range of about 200 C. to about 350 C., with evolution of carbon dioxide from the reaction mixture.

5. A corrosion inhibitor comprising the product obtainable by reacting between about one and about two mols o1 maleic anhydride and about one mol of a pyridine compound having a bolng range of from about 250 C. to about 350 C., with evolution of carbon dioxide from the reaction mixture.

6. A pickling bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the reaction product of a pyridine compound and maleic anhydride.

7. A pickling bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a tar base with evolution of car bon dioxide from the reaction mixture.

8. A pickling bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a pyridine compound having a boiling range of from about 200 C. to about 360 C.', with evolution of carbon dioxide from the reaction mixture.

9. A pickling bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a tar base having a specific gravity of from about 1.061 to about 1.135, the major portion of which distills within the range of about 200 C. to about 350 C., with evolution of carbon dioxide from the reaction mixture.

10. A pickling bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the product obtainable by reacting about one mol of a pyridine compound having a boiling range of from about 250 C. to about 350 C. with between about one and about two mols of maleic anhydride with evolution of carbon dioxide from the reaction mixture.

11. A pickling bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising common salt and the product obtainable by reacting maleic anhydride and a tar base having a specific gravity of from about 1.061 to about 1.135, the major portion of which distills within the range of from about 200 C. to about 350 C., with evolution of carbon dioxide from the reaction mixture.

12. The process of pickling metals which comprises subjecting the metal to the action of a bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the reaction product of a pyridine compound and maleic anhydride.

13. The process of pickling metals which comprises subjecting the metal to the action of a bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a tar base with evolution of carbon dioxide from the reaction mixture.

14. The process of picking metals which comprises subjecting the metal to the action of a bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a pyridine compound having a boiling range from about 200 C. to about 360 C., with evolution of carbon dioxide from the reaction mixture.

15. The process of pickling metals which comprises subjecting the metal to the action of a bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the product obtainable by reacting maleic anhydride and a tar base having a specific gravity of from about 1.061 to about 1.135, the major portion of which distills within the range of about 200 C. to about 350 0., with evoution of carbon dioxide from the reaction mixture.

16. The process of pickling metals which comprises subjecting the metal to the action of a bath comprising a dilute solution of a mineral acid capable of readily dissolving iron oxides and a corrosion inhibitor comprising the product obtainable by reacting about one mol of a pyridine compound having a boiling range from about 250 C. to about 350 C. with between about one and about two mols of maleic anhydride with evolution of carbon dioxide from the reaction mixture.

17. A substantially non-iron dissolving solution comprising a mineral acid capable of readily dissolving iron oxides and a product obtainable by reacting maleic anhydride and a tar base with evolution of carbon dioxide.

18. A substantially non-iron dissolving solution comprising a mineral acid capable of readily dissolving iron oxides and a product obtainable by reacting maleic anhydride and a tar base having a specific gravity of from about 1.061 to about 1.135, the major portion of which distills within the range of from about 200 C. to about 350 C., with evolution of carbon dioxide from the reaction mixture.

PERCY J. COLE. 

